Reaction means for rotating ammunition projectiles at low speeds



IN VEN TOR. WILLIAM J. KROEGER Filed Feb. 28, 1952 W. J. KROEGER REACTION MEANS FOR ROTATING AMMUNITION PROJECTILES AT LOW SPEEDS May 28, 1%57 ATTORNEYS:

REACTIONMEANS FOR ROTATING AMMUNI- TION PROJECTILES AT LOW SPEEDS William'J. Kroeger, Philadelphia, Pa., assignor to the .United States of America as represented by the Secretary of the Army Application February 28,1952, Serial'No. 274,044 1 Claim. (Cl. 102-'51) (Granted under Title 35, U. s. Code (1952), sec. 266) Thie; invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

Recent developments in the military weapon and ammunition art have led to the use of what has been termed the shaped charge. This type of projectile, among others, requires a very minimum amount of spin while in flight, as too much spin has been known to spoil'its armor-piercing or other such desired characteristics. On the other hand, some small amount of spin is necessary in order to offset the normal lack of symmetry in the manufactured parts, and more fully discussed in application Serial No. 224,435, filed May 3, 1951 (now abandoned). In the case of the gun and ammunition herein illustrated (Fig. 1), a recoilless firing device similar to that shown by Kroeger-Musser U. S. Patents 2,466,714 and 2,472,111 but employing a more recent type of projectile which is finstabilized, it has been determined that a suitable compromise between these two requirements is on the order of -20revolutions per second (R. P. 8.). Prior to my invention, the conventional means for causing projectiles to rotate, e. g. mechanical engagement between a rotating band and a rifled gun bore, caused rotation at a speed which far exceeded these relatively low speeds.

Broadly stated, therefore, it is the principal object of my invention to provide a means for imparting a controlled, low rotative speed to projectiles fired from a rifled or smooth bore gun.

Another object is to accomplish such means-in a fast, economical manner with a minimum amount of alteration being required for the ammunition and none for the gun.

These and other-related objects are accomplished by my invention as will be seen by reference to the following specification and the annexed drawings, wherein:

.Fig. 1 shows portions of a barrel and breech, in longitudinal section, of a n'fled recoilless gun, together with a plan view of .an ammunition round whose projectiles bourrelet portion is provided with a series of reaction engines, in the form of specially designed nozzles, to effect a low speed in accordance with my invention;

Fig. 2 is view similar to Fig. 1 except that the rearward part of the ammunition rounds cartridge case has been eliminated, and the reaction engines are each comprised of a reservoir and a nozzle;

Fig. 3 depicts an enlarged portion of the reaction engines nozzles and the opposed wall of the smooth bore gun barrel as seen from line 33 of Fig. 1;

Fig. 3A is an illustration identical with that of Fig. 3 except that the bore of the gun barrel bears rifiing lands and grooves such as are shown in Fig. 2; and

Fig. 4 is a much enlarged showing of the reaction engine portion (as shown in Fig. 2) on which has been super-imposed the lands of a rifled gun barrel just as if the view was through the guns rear wall.

From the drawings and the following description it will be noted that I have accomplished the'aforementioned objects by uniquely providing in the projectiles bourrelet portion reaction engines consisting of nozzles, sometimes supplemented with reservoirs, which preferably are broached in the projectiles surface. These engines, by providing ridges in the projectiles walls which are at an angle with respec-t to the line of flight through the gun, form channels or nozzles for the passage of some of the forwardly moving powder gases relative to the projectile and cause the projectile to spin by virtue of the transverse reaction elfect exerted by these escaping gases. In

this way, some of the tremendous energy which is avail-- able in the propellent gases is used to spin the projectile. Since some of the gases which evolve when theammun ition is fired will course through the length of the barrel between the projectile and the wall of 'smooth-bored barrels, or between the projectile and the lands and grooves of rifled barrels, those gases are caused to expand through the nozzles and exert rotative force against the walls thereof.

For a better understanding of my invention the various" components shown in the drawings will now be identified and their functions briefly described. The conventional gun shown is of a recoilless type (although obviously my invention need not be limited to use with such guns), of

which two main examples are illustrated: the one shown in Figures 2, 3A and 4 has a barrel 8, rifled'with lands 9 and grooves 10, and a rearwardly expanding chamber '11.

The other, which is shown in Figs. 1 and 3', has a smooth bore barrel 8a and chamber 11a. The ammunition round is substantially the same regardless of the gun typeinf which it is to be used, except that in'accordance with my invention itsprojectile may be'modified in a number of different ways of which one form is representedat 12in Figs. 1, 3 and 3A, While another is depicted at 12a in Figs 2 and 4. The projectile has an extension 13 which rests inside a cartridge case 14. Extension 13 optionally bears a number of flight-stabilizing fins 15 (only one is shown).

Propellent powder 16 surrounds the projectile extension. Although the illustrated ammunition is of a special form to which my invention obviously need not be limited, it has been selected as an example primarily because it represents a type which happens to be most effective when its projectile is given a minimum spin and,-ther efore, my improvements are ideally suited thereto.

The projectile is provided with a bourrelet 20 which is the largest diametered' portion of the projectile and, thus, in well known manner, serves as the -riding surface which contacts the smooth bor e wall of barrel 8a or end (toward the projectiles base) and continuing par tially or entirely across the bourrelet, even onto the projectiles nose,are slot-like helical-nozzles 22 cut by any suitable means such as by a breaching machine. The projected area of these nozzles and the angle 0 (see Fig. 4) between these nozzles and the axial center-line of the projectile may be varied, depending upon the amount of projectile spin desired, the weight of the projectile to be spun, the force to be supplied by a particular propellent powder, the ballistic relationships of the projectile to the gun, etc. This angle may be determined quite readily either by calculation or empirically, as desired. Thus, the nozzles are each disposed along a line which forms an acute angle with or within an imaginary plane which is inclined with respect to the axial centerline of the projectile but which is inclined, in an opposite sense, as compared with the inclination of the imaginary planes including the guns rifiing lands with respect to the guns axial center-line. In addition, the nozzles are terminated at their forward ends in a plane which is disposed normal to the axial center line of the projectile and they are arranged symmetrical about the center line to preserve exterior ballistic control. Optionally, the rearward por- Patented May as, 1951 tion or entrance into nozzles 22 may be expanded to form reservoirs 23, as shown in Figs. 2 and 4.

The operation of my invention should, by now, be apparent. The forwardly moving gases evolved upon ignition of propellent powder 16 will, in the case where rifled gun barrels are employed, be caused by the guns lands 9 to flow (as indicated by arrows 26 in Fig. 4) through rifling grooves along a line which forms the angle a with the projectilesaxial center line. Not all of the gases will thus be channeled by lands 9 and grooves 10 for some will sweep axially over the lands and approach nozzles 22 as indicated by arrow 27 in Fig. 4. The gases are thus not directionalized at first, but are given direction upon entering nozzles 22, moving as indicated by arrow 28 in Fig. 4.

The gases enter the nozzles at essentially the pressure and temperature of the main body of powder gas, then expand through the nozzles to acquire sonic velocity (approximately 3000 feet per second). The reaction on the nozzles exerted by the gas in accelerating itself to sonic velocity creates a torque which acts to rotate the projectile and effectively to decelerate slightly the projectiles forward motion in the gun barrel. tially may be interpreted as a result of the decreased crosssection presented by the projectile to the powder gases; i. e., there isless projectile surface area on which the gas can act, than there would be if slot-like nozzles 22 were not, cut into the projectile wall.

Reservoirs 23 optionally are employed to collect larger volumes of gas than might otherwise be led to enter nozzles 2 2, and they serve to bring the gases to rest with:

respect to the shell at essentially the pressure and temperature of the main body of powder gas. It should further be understood that the reservoirs may be used in conjunction with rifled gun barrels (as shown in Figs. 2 and 4) or with smooth barrels (not shown in this connection). Similarly, the simple nozzle design shown used with a smooth barrel in Figs. 1 and 3, may also be employed with rifled barrels as in Fig. 3A.

In addition to accomplishing the principal objective of imparting spin to projectiles at a low rate of speed, the presence of such reservoirs and nozzles in the bourrelet of the projectile has been found to have a further desirable effect in minimizing and suppressing undesirable yawing or balloting motions of the projectile during its passage through the bore. This contributes an additional factor leading to improved accuracy of the projectile in flight. These two uses of the reservoir thus naturally supplement each other in producing accurate, stable flight exterior to the bore.

Although the foregoing description of my inventions operation principally has been stated with reference to its use with rifled gun barrels, it is to be noted that my improvements work equally well in conjunction with smooth bore gun tubes such as are shown at 8a in Figs. 1 and 3. Since nozzles 22 are cut either entirely across the bourrelet The latter effect essen- 20 (as shown in Fig. 1) or partially across the forward portion thereof from the leading or forward end of reservoirs 23 (as shown in Fig. 2), some of the powder gases travelling forwardly from cartridge case 14 must enter the nozzles. Thus, the aid of gun barrel riflings to channel the gas towards the nozzle actually is not required.

It will, therefore, be noted that by my invention an effective means has been provided for imparting a controlled, low rotative speed to projectiles fired from'a rifled or smooth bore gun, and this means can be accomplished in a fast, economical manner with a minimum amount of alteration being required for otherwise conventional ammunition and none for the gun. Thus, one and the same weapon is capable of firing projectiles rotated slowly by my herein described novel means, or rotated at much higher speeds by such prior art devices as mechanical engagement of rotating bands with gun barrel riflings, etc. This, of course, makesit possiblerfor a gunner to put his weapon to dual usage-an invaluable asset in the fieldwithout requiring different guns or special modifications thereof to fire projectiles at differing rotative speeds.

My invention will likewise be recognized as extensive in its adaption and is not to be restricted to the specific forms here shown by way of illustration.

I claim:

In an ammunition projectile to be fired from a rifled gun barrel, means for rotating the projectile at low speeds so as to offset the normal lack of symmetry of its components, comprising, a bourrelet which is circumferentially located on the projectile and whose external diameter forms a readily slidable fit with the gun barrels bore, shallow reservoirs cut into the wall of the bourrelet forwardly from its rear end, and slot-like nozzles cut into the bourrelet from the forward end of said reservoirs across thebourrelet to the forward end thereof on a line which forms an acute angle and inclined with a line parallel to the axial center-line of the projectile, the inclination thereof being disposed in an opposite sense to the inclination of the guns rifiing with respect to the guns axial center-line, and said nozzles terminating forwardly in a plane disposed normal to said axial center-line,

whereby some of the gases used to propel the projectile from the gun barrel will be initially collected in the reservoirs and then be directionalized so as to flow into and through said nozzles, effecting a reaction en route so as to cause the projectile to rotate.

References Cited in the file of this patent UNITED STATES PATENTS 939,682 Gleason Nov. 9, 1909 1,341,844 Dougan June 1, 1920 FOREIGN PATENTS 39,273 Austria June 1, 1909 597,633 Germany May 28, 1934 609,594 Germany Feb. 18, 1935 

